This invention relates to a method of making a new coherent rigid solid material particularly adapted for use as an insulating material.
Heat insulating materials are known which are prepared from fillers having at least a 75% reactive expanded perlite content and alkaline ionic silicates. Such materials are formed and cured so as to enable the perlite fraction of the filler to react with the silicate to produce a crystalline reaction product. U.S. Pat. No. 3,658,564 discloses such a material and a method of making such a material.
The material of U.S. Pat. No. 3,658,564 is made by using an extended curing period of at least three days and preferably seven to achieve relative water insensitivity. Moreover curing is accomplished under carefully controlled conditions of humidity and temperature during this period. The required curing creates some difficulties in the large scale production of the high temperature insulating material.
In addition, the material of U.S. Pat. No. 3,658,564 must be made with specific SiO.sub.2 :K.sub.2 O and SiO.sub.2 :Na.sub.2 O ratios in the alkaline ionic silicates. In particular, water resistive or insensitive products require SiO.sub.2 :Na.sub.2 O ratios of 3:1 to 4:1 and SiO.sub.2 :K.sub.2 O of 2:1 to 2.6:1 to achieve a water insensitive product. Furthermore, the material of U.S. Pat. No. 3,658,564 has a rough surface texture which is undesirable from a cosmetic standpoint. The roughness is also undesirable because of the inability to provide intricate shapes, e.g., mitre joints.